1. Field of Invention
The present invention relates to a developing apparatus used in image forming apparatus such as copying machines, printers, or the like, using electronic photography and, more particularly, relates to a developing apparatus in which a latent image on a photosensitive body is developed in the process in which toner is formed on a developing roll, and a toner cloud is formed in a developing region through an electrode wire which is arranged so as to be near to a layer of the toner formed on the developing roll or so as to be in contact with the layer of the toner.
2. Description of Prior Art
Heretofore, Unexamined Japanese Patent Publication Hei-1-304477 has described a developing apparatus as described above.
Further, Japanese Patent Unexamined Publication No. Hei-3-113474 has described a developing apparatus in which a latent image on a surface of a photosensitive body is developed through the process in which a toner layer is formed by feeding a two-component developer to a developing roll by using a toner supply roll and by transferring toner onto the developing roll, and a toner cloud is formed through an electrode wire which is arranged so as to be near to the toner layer or so as to be in contact with the toner layer.
According to these types of developing apparatuses, for the achievement of highly efficient developing, a toner cloud is formed in the neighborhood of the electrode wire by means of applying an AC voltage to the electrode wire which is arranged so as to be near to the toner layer formed on the developing roll or so as to be in contact with the toner layer, or by any other like means.
In the following, the above-mentioned developing apparatus, that is, a developing apparatus in which a latent image on a surface of a photosensitive body is developed by forming a toner cloud through electrode wire, will be described with reference to FIGS. 13 and 14.
In FIG. 14, the developing apparatus 100 has a developing vessel 101 for storing a predetermined amount of a developer. A developing roll 102 and a toner supply roll 103 are mounted so as to be rotatable in the inside of the developing vessel 101. The developing roll 102 can be rotated in both of same and opposed directions with respect to the direction of movement of a photosensitive body D. Similarly, the toner supply roll 103 can be also rotated in both of same and opposite directions with respect to the direction of rotation of the developing roll 102, in relation to the arrangement of a limiting member which will be described later. In FIG. 14, the developing roll 102 is rotated in the direction reverse to the direction of movement of the photosensitive body D, whereas the toner supply roll 103 is rotated in a same direction with the developing roll 102 so that they are moved relatively reversely at a proximate portion.
An auger 104 for mixing and stirring the developer is mounted in the inside of the developing vessel 101 so as to be rotatable.
An electrode wire W is disposed between the developing roll 102 and the photosensitive body D. The electrode wire W is automatically departed from the developing roll 102 by a toner layer formed on the developing roll 102, so that the distance between the electrode wire W and the developing roll 102 becomes equal to the thickness of the toner layer. The distance between the electrode wire W and the developing roll 102 is generally from about 5 .mu.m to about 30 .mu.m. Opposite end portions of the electrode wire W are mounted slightly inward with respect to a cylindrical surface containing a surface of the developing roll 102 containing the toner layer.
In FIG. 14, a two-component developer constituted by carrier and toner is put up to the height h shown in the drawing. The developer is attracted to a surface of the toner supply roll 103 by magnetic force of a magnet 103a fixed in the inside of the toner supply roll 103 and is conveyed toward the developing roll 102 by rotation of the toner supply roll 103. The developer on the toner supply roll 103 is measured by a limiting member 105 so intermediately that a predetermined amount of the developer can be continuously conveyed to a region between the toner supply roll 103 and the developing roll 102.
A DC bias voltage source 106 and a DC bias voltage source 107 are connected to the toner supply roll 103 and the developing roll 102, respectively. A voltage of about -400 volts and a voltage of about -300 volts are applied to the toner supply roll 103 and the developing roll 102 by these electric sources 106 and 107, respectively, so that an electrostatic field is formed between the developing roll 102 and the toner supply roll 103 to thereby attract toner particles from the toner supply roll 103 to the developing roll 102. Thus, a toner layer of even thickness is formed on the surface of the developing roll 102.
An AC bias voltage is applied to the electrode wire W by an AC source 108. An AC field is formed between the electrode wire W and the developing roll 102 by the applied AC bias voltage, so that toner is separated from the surface of the developing roll 102. Thus, a toner cloud is formed around the electrode wire W. The AC bias voltage is from about 200 bolts to about 1000 bolts as peak voltage at a frequency of about 3 kHz to about 15 kHz.
The voltage of about -300 bolts from the AC bias source 107 is applied to the developing roll 102, so that an electrostatic field is formed between the developing roll 102 and the photosensitive body D. As a result, the toner particles separated from the toner cloud formed around the electrode wire W are attracted to a latent image recorded on the photosensitive body D. In such apparatus, the electrode wire W or the developing roll 102 may be coated with a dielectric material to assist in preventing the applied AC voltage from being short-circuited.
The toner supply roll 103 supplies new toner again to a portion where toner is removed from the developing roll 102 by development. At this time, a predetermined amount of toner substantially having a constant electric charge can be accumulated on the developing roll 102 by combining while adjusting the distance between the developing roll 102 and the toner supply roll 103, the amount of the two-component developer on the toner supply roll 103, the magnetic characteristic of the toner supply roll 103, the rotating speed ratio of the toner supply roll 103 to the developing roll 102, the voltages of the DC bias sources 106 and 107 and the electrical conductivity of the carrier contained in the two-component developer.
According to the developing apparatus 100 described above with reference to FIG. 14, for the achievement of highly efficient developing, a toner cloud is formed in the neighborhood of the electrode wire W by means of applying an AC voltage to the electrode wire W which is arranged so as to be near to a toner layer formed on the developing roll 02 or so as to be in contact with the toner layer.
In the following, the configuration of the periphery of the electrode wire W will be described with reference to FIG. 13. FIG. 13 is a horizontal sectional view of the above-mentioned developing apparatus 100.
An electrode supporting member 110 is fixed to one side wall 101a of the developing vessel 101. The electrode supporting member 110 is constituted by a bracket 111 fixed to the side wall 101a, and a wire fixing member 112 and a wire positioning member 113 which are supported by the bracket 111.
An electrode supporting member 115 is also fixed to another side wall 101b of the developing vessel 101. The electrode supporting member 115 is constituted by a bracket 116 fixed to the side wall 101b, and a wire fixing member 117 and a wire positioning member 118 which are supported by the bracket 116.
The above-mentioned electrode wire W is suspended between the electrode supporting members 110 and 115. The electrode wire W is guided by the wire positioning members 113 and 118 while being kept in a tensioned state by a tension spring S provided for application of a tensile force. Outer end portions of the electrode wire W are fixed by the wire fixing members 112 and 117. The electrode wire W is in contact with the wire positioning members 113 and 118.
If a foreign matter, such as a bulky toner particles, the aggregate of toner, dust fiber floating in air, paper fiber forming transfer paper, or the like, is trapped in the above-mentioned electrode wire W in a period of developing, it may be locally accumulated on the electrode wire W portion. Because this causes the production of stripes in the toner layer formed on the developing roll 102 or the local disorder in evenness of electric field formed by the bias voltage applied to the electrode wire W, there arises a problem in that various image defects may be brought.
At the time of maintenance, therefore, it is necessary to remove the so-called foreign matter accumulated on the electrode wire W.
The above-mentioned wire W is however selected so that its diameter is generally in a relatively narrow range of about 50 .mu.m to about 100 .mu.m (this range being limited to a lower limit by physical strength and to an upper limit by the distance between the photosensitive body and a donor member). As a result, the strength of the electrode wire W becomes so small that removal of the above-mentioned foreign matter without breaking of the wire is required at the time of maintenance.
The removal of the foreign matter in the condition that the electrode wire W and the developing roll 102 are proximate to each other, however, requires careful work. As a result, increase of working time, increase of working labor, and so on, are incurred. In the case where the electrode wire W is broken by mistake, wire exchanging work is required so that the number of working steps at the time of maintenance increases. As a result, the burden on the user becomes heavy.